1. Field of the Invention
Methods consistent with the present invention relate to the digital rights management (DRM) of a home network and, more particularly, to key management using a hierarchical node topology, and registering and deregistering a user using the same.
2. Description of the Related Art
Generally, digital content is transmitted from a content provider to a user who can use the digital content only after acquiring a proper right by paying for the digital content.
FIG. 1 illustrates a home network. Referring to FIG. 1, a content provider CP transmits content to a home network HN via a transmission channel. The home network HN includes a home server HS and user devices D1, D2, and D3.
The home server HS initially receives the content via the transmission channel and controls the content to be used by the devices D1 through D3 according to a digital rights management (DRM) mechanism. That is, the home server HS is connected to the devices D1 through D3. The home server HS manages joining or withdrawing of an authorized user device to or from the home network HN and transmits the content only to an authorized user device, that is, to a currently registered device.
A domain indicates a set of user devices connected to a home server. The domain changes whenever the user devices join or leave the home network. In other words, the user devices connected to the domain are not fixed, and thus, a process of making a user device that left the home network unable to obtain any more content is required.
The content is encrypted using a content key and the content key is encrypted using a sharing key, and the content and the content key are transmitted to the user devices D1 through D3. Only user devices in the home network HN can acquire the sharing key.
As described above, the content is encrypted using the content key and the content key is distributed to only authorized users, thereby preventing unauthorized users from obtaining the content.
In recent years, the developments of home network technologies allow a user to exchange content between several user devices. Thus, the user sometimes desires to use content in all his user devices by paying for the content only once. However, if the content can be moved freely between devices in a reproducible way, an unauthorized user can acquire and use the content. Accordingly, there is a growing need to improve the home network technology so that content can be exchanged between user devices over a home network of an authorized user while preventing an unauthorized user from acquiring the content and using the content even if the unauthorized user acquires the content.
In particular, the U.S. Federal Communications Commission (FCC) requires, as of July 2005, a standard for digital broadcasting technology by which a 1-bit broadcast flag (BF) should be included into high-definition (HD) content to be broadcast through digital broadcasting throughout the U.S., so that content protection can be enabled when the BF of content is 1 to prevent unauthorized users from using the content. Therefore, there is an urgent need for a method for securely using digital broadcast content between a home server and a user device.